1. Field of the Invention
This invention relates to a method and an apparatus for detecting gas components in the oil in an oil-filled device, and particularly to a method and an apparatus for detecting gas components in the oil in an oil-filled device, which are suitable for separating and detecting dissolved gas components in a degasified insulating oil in the oil-filled device to find an abnormality of the device.
2. Description of the Prior Art
It is well known that when an abnormality such as local overheating or partial discharging occurs in an oil-filled electric device such as transformer, rectifier, capacitor, cable, etc., the insulating oil or solid insulated article is decomposed to produce the gases of H.sub.2 and hydrocarbon types such as CH.sub.4, C.sub.2 H.sub.2, C.sub.2 H.sub.4, C.sub.2 H.sub.6, etc., and/or gases of other type such as CO, CO.sub.2, etc., and most of these gases stady dissolved in the insulating oil. Therefore, if the gases dissolved in the insulating oil in an oil-filled electric device are constantly monitored, it is possible to detect abnormality in said device in its early stage.
Some of the present inventors proposed to detect gas components dissolved in the insulating oil in an oil-filled device, where the dissolved gas components are separated from the insulating oil in an oil-filled device, the separated gas components are stored in a gas storing chamber, or in a gas calibration tube connected to the gas storing chamber, and the stored gas components are led to a gas separation column from the gas storing chamber or the gas calibration tube to detect the gas components by a gas detector (Japanese Laid-open Patent Application No. 56-162049, U.S. patent application Ser. No. 265,656 now U.S. Pat. No. 4,402,211).
However, when the dissolved gas components are detected by the gas detector in combination with a device for separating gas components from an insulating oil through a gas-permeating material, and when a degasified oil is used as the insulating oil for an oil-filled device, for example, in a transformer, a subatmospheric pressure prevails in the gas storing chamber or in the gas calibration tube, because the gas components in the gas storing chamber or in the gas calibration tube permeate in a reversed direction through the gas-permeating material from the gas-storing chamber into the degasified insulating oil, and absorbed therein owing to the principle of equilibrium. The subatmospheric pressure is thus a problem. That is, in the detection of gas components it is not advantageous from the viewpoint of cost to quantitatively determine the respective gas components by way of integrated output values, and it is the ordinary expedient to make quantitative determination by way of peak output values. However, if a subatmospheric pressure prevails in the gas-storing chamber or in the gas calibration tube in the quantitative determination of the respective gas components by way of peak output values by gas chromatography, the peak output values tend to be larger under the subatmospheric pressure than under the normal pressure. That is, correct peak output values cannot be measured. This is because the peak output values of the respective gas components increase in proportion to the degree of subatmospheric pressure prevailing in the gas-storing chamber or in the gas calibration tube. As shown in FIG. 1, such relations are observed for H.sub.2, CO and CH.sub.4 gas components dissolved in insulating oil that the peak output values in mV are increased in proportion to the degree of subatmospheric pressure in a gas-storing chamber or in a gas calibration tube.
Particularly in the case of detecting gas components having a short gas chromatographic detection time, the peak output values are greatly influenced by the degree of subatmospheric pressure. In the detection of permeated gas components, the permeated gas components are pushed off from the gas calibration tube by a carrier gas and without substantial diffusion of the permeated gas components into the carrier gas due to a very short time, the pushed gas enters into the gas chromatographic device as a zone under a subatmospheric pressure, giving the influence of the subatmospheric pressure to the peak output values. Thus, it has been necessary in the quantitative determination of permeated gas components to measure the pressure prevailing in a gas-storing chamber or in a gas calibration tube to make the necessary correction of pressure. However, this will not only complicate the measuring operation, but also requires additional special devices such as a pressure gage, etc.
The degasified insulating oil usually still contains about 0.5 to about 2.0% of gas components, and thus a subatmospheric pressure prevails in the gas-storing chamber or in the gas calibration tube in terms of a pressure ratio of about 0.05 to 0.1 to the normal pressure as unity. Thus, a subatmospheric pressure prevailing in the gas-storing chamber or in the gas calibration tube has been a problem.